Automatic volume control



y 1939- k. A. CHITTICK 59, 80

AUTOMATIC VOLUME CONTROL, 7

Original Filed Dec. 16, 1933 O Emma m T m V QWkQQ E E O b a WM n I I A kmkuxm R gHHTICK Q35 ESQ w Y bk QQQQQR N MEEEQ kw QNN Patented May 23, 1939 AUTOMATIC VOLUlIE CONTROL Kenneth A. Chittick, Haddonfield, N. J., assignor to Radio Corporation of America, a corporation of Delaware Original application December 16, 1933, Serial No.

702,674. Divided and this application November 9, 1936, Serial No. 109,873

3 Claims.

My present invention relates to gain control arrangements for high frequency signalling systems, and more particularly to automatic volume control circuits for radio receivers, and is a division'of my application Serial No. 702,674, filed December 16, 1933, Patent No. 2,092,500, September '7, 1937.

One of the main objects of my present invention is to provide an automatic volume control arrangement for a radio receiver wherein a direct current potential variation in a positive"'cold electrode circuit of the intermediate frequency amplifier is employed for regulation of the gain of a preceding high frequency transmission network.

Still other objects of the present invention are to improve generally the simplicity and efficiency of automatic volume control circuits, and to particularly provide a receiver wherein automatic volume control bias is secured without the use of an auxiliary control tube and which automatic volume control is constructed and assembled in a radio receiver in an economical manner.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, will best be understood by reference to the accompanying drawing, wherein several circuit arrangements of the present invention are shown and described.

In the drawing:

Fig. 1 diagrammatically shows one circuit arrangement embodying the present invention, and

Fig. 2 shows a modified form of the invention.

Referring now to the accompanying drawing, wherein like reference characters in the different figures designate similar circuit elements, there is shown in Fig. 1 one embodiment of the invention, the embodiment comprising a superheterodyne receiver of conventional construction. The receiver, since conventional and well known to those skilled in the art, will only be briefly described. It comprises one, or more, stages of radio frequency amplification, these stages being .uni-controlledly tunable in any well known manner. The input to the amplifier includes the usual signal collecting circuit, and, although shown as a grounded antenna system, is to be clearly understood as being capable of replacement by any other well known collector of signal energy.

The amplifier network is followed by a network which is designated 1st detector-local 050., but it is to be clearly understood that this network may embody a separate local oscillator and a separate first detector, or may be of the combined oscillator-detector type. In many cases, as where compactness is desired, this network may be a combined oscillator-detector circuit of the type disclosed and claimed by J. C. Smith in applica- 5 tion Serial No. 654,421, filed January 31st, 1933. In the latter case the preceding network can be omitted, and the automatic volume control arrangement to be hereinafter described applied to the signal control electrode of the combined oscil- -10 cludes a pair of coupled resonant circuits, both tuned to the operating intermediate frequency. The amplified intermediate frequency energy is transmitted to the succeeding second detector through a coupling network which includes coupled resonant circuits tuned to the operating intermediate frequency. The second detector output may be impressed upon an audio frequency amplifier, and the amplified audio frequency energy reproduced in a reproducer of the electromagnetic or electrodynamic type.

It is to be clearly understood that the power supply source of the receiver may be the usual 21 power supply filter succeeding the rectifier tube when used with an alternating current supply, but the power supply source may, also, be a network adapted for use directly with a commercial direct current or alternating current supply.

In Fig. 1 is shown the tube 59 which includes 1 two sections that perform different functions in one envelope. This tube is of the type known as 61W, and comprises a pentode section and a triode section having a common cathode. grid 5! and the control grid 52, of the pentode and triode sections respectively, are connected together through a condenser 53. The cathode of tube 50 is connected to point P1 on the divider resistor 54; the control grid BI is connected through lead 55 to point P2 on the divider for the normal grid bias; and the anode and screen of the pentode section of tube 5!! are connected to proper positive potential points. The anode of the triodesection of tube 55!, which triode section I The control The cou- 5 to point P3 on divider 54 through lead 56 to obtain the proper negative grid bias.

The amount of this bias may be sufficient to provide current in resistor R1 for the residual grid bias for the amplifier tubes, or it can be of such a value that several volts of intermediate frequency voltage must be applied to the control grid before any automatic volume control bias is developed.

In operation, when signal is applied to both the control grids 5| and 52 is parallel the effective bias on the automatic volume control section of tube is reduced as the signal is increased until current flows in resistor R1 and generates control voltage. This volume control bias is applied to the preceding radio frequency amplifier, or amplifiers, and may also be applied to the intermediate frequency amplifier 60. When bias is applied to the tube 60' the amount of bias desired to make the overall amplifier flat against signal voltage is obtained by tapping a portion of resistor R1 for this bias. This last named arrangement is disclosed in co-pending application Serial No. 642,544, filed November 14th, 1932, of

Chittick and Carlson, Patent No. 2,074,014, March' 16, 1937. Here again the voltage supply may be obtained across a bleeder resistor, and not across circuits shunting the rectifier filter system. It is not necessary to explain the remaining portions of the circuit in detail, since they are well known to those skilled in the art from their diagrammatic showing.

In the modification shown in Fig. 2, there is shown an arrangement wherein the tube 60 is substituted for the tube 50 of Fig. 1. The tube til is of the type known as 2A7, and the various tube electrodes are supplied with proper operating voltages as shown in Fig. 2, and as illustrated in Fig, 1. Signal voltage is applied to both control grids GI and 62 connected in parallel through the coupling condenser 63. When the signal voltage increases, the effective bias on the automatic volume control grid electrode is reduced and current fiows in resistor R2 thus generating volume control bias.

This reduction in effective bias increases the anode current of the intermediate frequency amplifier section of tube 60 so that the tube also acts as a noise suppressor circuit. The additional intermediate frequency amplifier tube 60' may be included between the second detector and tube 60, as shown in Fig. 1. No further description of Fig. 2 is believed necessary in view of the fact that it functions in a manner similar to Fig. 1, with the exception of the noise suppressor function.

While I have indicated and described several systems for carrying my invention into effect, it

,will be apparent to one skilled in the art that my invention is by no means limited to the paricular organizations shown and described, but hat many modifications may be made without departing from the scope of my invention, as set forth in the appended claims,

What I claim is:

1. In combination with a high frequency amplifier to be controlled as to gain, an amplifier in-- cluding a signal input electrode connected to the controlled amplifier for the transmission of signal energy from the controlled amplifier to the second amplifier, a potential supply source including a bias resistor, a control grid in the second amplifier receiving signals from the first amplifier, means for connecting the control grid and cathode of the second amplifier to points on said resistor such that the control grid is normally negative with respect to the cathode, said second amplifier including an auxiliary electrode, an impedance connected between said auxiliary electrode and a potential point on said supply source which is positive with respect to said points, and a conductive connection between a point on said impedance and a gain control electrode of said controlled amplifier said last point becoming increasingly negative with respect to said positive point as the signal amplitude increases.

2. In combination, a signal transmission tube, a tube having'an amplifier section and a rectifier section, said rectifier section including a pair of input electrodes and an independent output electrode, means impressing radio frequency signals from the transmission tube on the input electrodes of both sections, an impedance in the output electrode circuit of the rectifier section, means impressing the direct current voltage developed across the impedance by rectified signal current upon the transmission tube as a gain control voltage, and means biasing the rectifier section input electrodes to prevent current flow through the impedance in the absence of signals, the electrodes of the two sections being in a comrnon electron stream between a common cathode and the amplifier section output electrode.

3. In combination, a signal transmission tube, a tube having an amplifier section and a rectifier section, said rectifier section including a pair of input electrodes and an independent output elec- I trode, means impressing radio frequency signals from the transmission tube on the input electrodes of both sections, an impedance in the output electrode circuit of the rectifier section,

means impressing the direct current voltage developed across the impedance by rectified signal current upon the transmission tube as a gain control voltage, means biasing the rectifier section input electrodes to produce minimum current flow through the impedance in the absence of 

